I was asked to look at the remaining unicode text issues remaining on
OS X. It seems there are some issues specific to this operating
system, and some general:

a) Uppercases character umlaut (e.g. Ü) are not rendered correctly in
the user interface, they do show in 3D text and the text editor.
Appears to be a text rendering problem that would happen on all
platforms?
b) The text editor does not use the new event->utf8 at all yet, still
only event->ascii. It seems the text editor may need major rewriting
to support utf8, so this is not intended to work yet?

Two OS X issues:

c) Typing with dead keys (e.g. ¨ + o => ö) didn't work for me. I
managed to get it working using NSTextInput, patch here if people want
to test, I'm not very confident that this doesn't break something, so
some testing would be great: http://www.pasteall.org/25983/diff
d) Typing e.g. ` + o to get ò seems to break various shortcut keys
(same issue exists in 2.59). For example pressing ctrl+q does nothing
after this, changing window focus or typing other characters makes it
work again.